Pneumatic tire

Abstract

The present invention addresses the problem of providing a pneumatic tire in which a reduction in tire performance is mitigated despite using polyamide fibers with low amide density. The solution is a pneumatic tire characterized by comprising a carcass layer (50), belt layers (60A, 60B), and a belt reinforcement layer (70A), wherein reinforcing cords (50-1, 70A-1) in the carcass layer (50) and / or the belt reinforcement layer (70A) contains polyamide fibers having an amide density of 14.0 or less, and (i) when a gauge thickness A from the outer circumferential surface on the tire inner-surface side of the reinforcing cords (50-1) of the carcass layer (50) to the tire inner surface is measured at 100 equally spaced points, the average of the gauge thickness A is 1.5 mm or less, or (ii) when a gauge thickness D from the outer circumferential surface on the tire outer-surface side of the reinforcing cords (70A-1) of the belt reinforcement layer (70A) to the tire outer surface is measured at 100 equally spaced points, the gauge thickness D is 6.0 mm or less at 80% of the measurement points or more.

Description

pneumatic tires

[0001] The present invention relates to a pneumatic tire.

[0002] Conventionally, a carcass layer including reinforcing cords is disposed inside a tire to reinforce the strength and rigidity of the tire, and a belt layer including reinforcing cords is disposed radially outward of the carcass layer. Furthermore, a belt reinforcing layer (also called a "cap layer") including reinforcing cords may be disposed radially outward of the belt layer to reinforce the belt layer. Among these tire components, organic fiber cords such as polyamide (nylon) fiber cords are widely used as reinforcing cords for the carcass layer and the belt reinforcing layer.

[0003] On the other hand, in recent years, there has been a demand for reducing the use of fossil resources such as petroleum and coal in order to reduce environmental impact. Therefore, the replacement of fossil-resource-derived organic fiber cords with biomass-derived (biological resource-derived) cords has also been considered, and such replacement must be able to sufficiently maintain tire performance. For example, Patent Document 1 listed below discloses a reinforcing ply having a reinforcing element containing a multifilament yarn made of nylon 4,10, and a pneumatic vehicle tire including such a reinforcing ply, and teaches that one of the two monomers of nylon 4,10 is based on a renewable raw material, making it environmentally friendly.

[0004] Special table 2019-511411 publication

[0005] As described above, polyamide fiber cords are widely used as reinforcing cords for carcass layers and belt reinforcing layers, and polyamide 6,6 (PA66) fiber cords are commonly used. However, polyamide 6,6, the raw material for polyamide 6,6 (PA66) fiber cords, is difficult to synthesize from biomass. In response to this, the present inventors conducted research and found that although polyamide 4,10 (i.e., nylon 4,10) can be easily synthesized from biomass, it has a lower amide density and fewer hydrogen bonds between amide bonds than polyamide 6,6, resulting in poor thermal properties. Therefore, organic fiber cords using such polyamide 4,10 exhibit reduced physical properties at high temperatures, and when such organic fiber cords are used in tires, tire performance is reduced.

[0006] Therefore, an object of the present invention is to provide a pneumatic tire that suppresses deterioration of tire performance while using polyamide fibers that have a lower amide density than polyamide 6,6 fibers.

[0007] The gist of the pneumatic tire of the present invention that solves the above problems is as follows.

[0008] [1] A pneumatic tire comprising: at least one carcass layer having a pair of bead portions, a pair of sidewall portions, and a tread portion continuous with both sidewall portions, and extending in a toroidal shape across the pair of bead portions; at least one belt layer disposed radially outward of a crown portion of the carcass layer; at least one belt reinforcing layer disposed radially outward of the belt layer; and at least one inner liner layer disposed adjacent to an inner surface of the carcass layer, wherein the carcass layer and the belt reinforcing layer comprise reinforcing cords, and the reinforcing cords of at least one of the carcass layer and the belt reinforcing layer comprise polyamide fibers having an amide density of 14.0 or less, and wherein, in a region of a tire cross section perpendicular to the tire circumferential direction where the belt reinforcing layer is disposed as viewed in the tire width direction, when the gauge thickness of the reinforcing cord of the carcass layer located innermost in the tire direction from the outer peripheral surface on the inner surface of the tire to the inner surface of the tire is measured at 100 equally spaced points, the average of the gauge thicknesses is 1.5 mm or less.

[0009] [2] A tire having a pair of bead portions, a pair of sidewall portions, and a tread portion connected to both sidewall portions, and comprising: at least one carcass layer extending in a toroidal shape spanning the pair of bead portions; at least one belt layer disposed radially outward of a crown portion of the carcass layer; and at least one belt reinforcing layer disposed radially outward of the belt layer, wherein the carcass layer and the belt reinforcing layer contain reinforcing cords, and the reinforcing cords of at least one of the carcass layer and the belt reinforcing layer contain polyamide fibers having an amide density of 14.0 or less, and wherein, in a region of a tire cross section perpendicular to the tire circumferential direction where the belt reinforcing layer is disposed as viewed in the tire width direction, when the gauge thickness from the outer peripheral surface on the tire outer surface side of the reinforcing cord of the belt reinforcing layer located outermost in the tire radial direction to the tire outer surface is measured at 100 equally spaced points, 80% or more of the measurement points have a gauge thickness of 6.0 mm or less.

[0010] [3] The pneumatic tire according to [1] or [2], wherein the reinforcing cords of both the carcass layer and the belt reinforcing layer contain polyamide fibers having an amide density of 14.0 or less.

[0011] [4] The pneumatic tire according to any one of [1] to [3], wherein the polyamide fiber having an amide density of 14.0 or less is a polyamide 4,10 fiber.

[0012] [5] The pneumatic tire according to any one of [1], [3] and [4], wherein the total thickness of the inner liner layer is 1.0 mm or less.

[0013] According to the present invention, it is possible to provide a pneumatic tire in which degradation of tire performance is suppressed even when using polyamide fiber having a lower amide density than polyamide 6,6 fiber.

[0014] It is a cross-sectional view of an example of a pneumatic tire according to a first embodiment of the present invention. It is a partially enlarged view of a tread portion of the pneumatic tire shown in Figure 1. It is a cross-sectional view of an example of a pneumatic tire according to a second embodiment of the present invention. It is a partially enlarged view of a tread portion of the pneumatic tire shown in Figure 3.

[0015] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The pneumatic tire of the present invention will be described in detail below by way of example based on embodiments thereof.

[0016] <Definition> In this specification, the term "biomass content rate" refers to the content rate of carbon derived from biomass, and is calculated using the following formula (1): Biomass content rate (%) = number of carbon atoms derived from biomass / total number of carbon atoms × 100 (1).

[0017] In addition, in this specification, the "biomass content rate of the entire cord" refers to the content rate of biomass-derived carbon in the entire cord, and is calculated using the following formula (2): Biomass content rate of the entire cord (%) = number of biomass-derived carbon atoms in the entire cord / total number of carbon atoms in the entire cord × 100 (2).

[0018] In this specification, the heat shrinkage of the reinforcing cord is measured in accordance with ASTM D885 and ASTM D4974, and is a value measured by heating at 177°C for 2 minutes.

[0019] In this specification, the "amide density" of a polyamide is calculated from the following formula (3): Amide density = number of amide groups in polyamide / number of atoms in the main chain of polyamide × 100 (3) Here, the "number of amide groups in polyamide" and the "number of atoms in the main chain of polyamide" are calculated from the "number of amide groups" and the "number of atoms in the main chain" in one repeating unit of the polyamide. For example, the amide density of polyamide 4 and polyamide 4,4 is 20.0, the amide density of polyamide 5,4 is 18.2, the amide density of polyamide 4,6 is 16.7, the amide density of polyamide 5,6 is 15.4, the amide density of polyamide 6 and polyamide 6,6 is 14.3, the amide density of polyamide 4,10 is 12.5, the amide density of polyamide 6,10 is 11.1, the amide density of polyamide 9,T is 10.5, the amide density of polyamide 10,10 is 9.1, and the amide density of polyamide 11 is 8.3.

[0020] In addition, in this specification, "biomass-derived" refers to being derived from biological resources such as plant resources, animal resources, and microbial resources, and is synonymous with "bio-derived."

[0021] The compounds described herein may be derived in part or entirely from fossil resources, biological resources such as plant resources, or recycled resources such as used tires, or may be derived from a mixture of two or more of fossil resources, biological resources, and recycled resources.

[0022] <Pneumatic tire> A pneumatic tire according to a first embodiment of the present invention has a pair of bead portions, a pair of sidewall portions, and a tread portion connected to both sidewall portions, and is equipped with: at least one carcass layer extending in a toroidal shape spanning the pair of bead portions; at least one belt layer disposed radially outward of a crown portion of the carcass layer; at least one belt reinforcing layer disposed radially outward of the belt layer; and at least one inner liner layer disposed adjacent to the carcass layer on the tire inner surface side. In the pneumatic tire of the first embodiment of the present invention, the carcass layer and the belt reinforcing layer contain reinforcing cords, and the reinforcing cords of at least one of the carcass layer and the belt reinforcing layer contain polyamide fibers having an amide density of 14.0 or less, and in a region of a tire cross section perpendicular to the tire circumferential direction where the belt reinforcing layer is arranged as viewed in the tire width direction, when the gauge thickness of the reinforcing cord of the carcass layer located radially innermost in the tire from the outer surface on the tire inner surface to the tire inner surface is measured at 100 equally spaced points, the average gauge thickness is 1.5 mm or less.

[0023]

[0003] The polyamide fiber having an amide density of 14.0 or less has a lower amide density and fewer hydrogen bonds between amide bonds than polyamide 6,6 fiber, resulting in poor thermal properties. Therefore, the physical properties of the polyamide fiber having an amide density of 14.0 or less deteriorate at high temperatures, and therefore the performance of a carcass layer and / or a belt reinforcing layer including a reinforcing cord containing a polyamide fiber having an amide density of 14.0 or less deteriorates at high temperatures. In contrast, in the pneumatic tire according to the first embodiment of the present invention, in the region where the belt reinforcing layer is disposed as viewed in the tire width direction of a tire cross section perpendicular to the tire circumferential direction, the gauge thickness of the reinforcing cord of the carcass layer located at the innermost side of the tire in the tire inner surface (i.e., the sum of the total thickness of the inner liner layer and the thickness of the coating rubber of the carcass layer located at the innermost side of the tire in the tire direction) is reduced to an average of 1.5 mm or less. This allows heat generated inside the tire during running to be quickly dissipated, suppressing an increase in the temperature inside the tire during running and suppressing a deterioration in the physical properties of the reinforcing cord containing a polyamide fiber having an amide density of 14.0 or less, thereby maintaining tire performance. Therefore, the pneumatic tire according to the first embodiment of the present invention is prevented from experiencing a decrease in tire performance even though it uses polyamide fibers having an amide density of 14.0 or less.

[0024] The gauge thickness from the outer peripheral surface of the tire inner surface side of the reinforcement cord of the carcass layer positioned innermost in the tire radial direction to the tire inner surface (i.e., the sum of the total thickness of the inner liner layer and the thickness of the coating rubber of the carcass layer positioned innermost in the tire radial direction) is preferably 1.0 mm or less on average. A pneumatic tire having an average gauge thickness of 1.0 mm or less is suitable as a racing tire.

[0025] a tire width direction of the tire, a tire width of the ...

[0026]

[0006] The polyamide fiber having an amide density of 14.0 or less has a lower amide density and fewer hydrogen bonds between amide bonds than polyamide 6,6 fiber, resulting in poor thermal properties. Therefore, the physical properties of the polyamide fiber having an amide density of 14.0 or less deteriorate at high temperatures, and therefore the performance of a carcass layer and / or a belt reinforcing layer including a reinforcing cord containing a polyamide fiber having an amide density of 14.0 or less deteriorates at high temperatures. In contrast, in a pneumatic tire according to a second embodiment of the present invention, when the gauge thickness of the reinforcing cord of the belt reinforcing layer located outermost in the tire radial direction is measured at 100 equally spaced points from the outer peripheral surface of the tire outer surface to the tire outer surface in a region where the belt reinforcing layer is disposed as viewed in the tire width direction of a tire cross section perpendicular to the tire circumferential direction, 80% or more of the measurement points have a gauge thickness of 6.0 mm or less. This allows heat generated inside the tire to be quickly dissipated, suppresses the temperature inside the tire from rising high during running, and suppresses deterioration in the physical properties of the reinforcing cord containing a polyamide fiber having an amide density of 14.0 or less, thereby maintaining tire performance. Therefore, the pneumatic tire according to the second embodiment of the present invention is prevented from experiencing a decrease in tire performance even though it uses polyamide fibers having an amide density of 14.0 or less.

[0027] (Carcass Layer and Belt Reinforcing Layer) The carcass layer and the belt reinforcing layer contain the reinforcing cords, and are usually formed by coating the reinforcing cords with a coating rubber.

[0028] -Coating Rubber- As the coating rubber for the carcass layer and the belt reinforcing layer, a rubber composition can be used in which a rubber component such as natural rubber or synthetic rubber is blended with a filler such as carbon black, an antioxidant, a vulcanizing agent such as sulfur, a vulcanization accelerator, etc.

[0029] The coating rubber preferably has (i) a loss tangent tanδ(24°C) of 0.15 or less when measured under conditions of a temperature of 24°C, an initial strain of 6%, an amplitude of ±1%, and a frequency of 52 Hz, and (ii) a loss tangent tanδ(60°C) of 0.10 or less when measured under conditions of a temperature of 24°C, an initial strain of 1.5%, an amplitude of ±1%, and a frequency of 52 Hz. By having the coating rubber (i) have a loss tangent tanδ(24°C) of 0.15 or less when measured under conditions of a temperature of 24°C, an initial strain of 6%, an amplitude of ±1%, and a frequency of 52 Hz, and (ii) have a loss tangent tanδ(60°C) of 0.10 or less when measured under conditions of a temperature of 60°C, an initial strain of 1.5%, an amplitude of ±1%, and a frequency of 52 Hz, the hysteresis loss of the coating rubber can be reduced from around room temperature to around the temperature during running, and heat generation inside the tire can be suppressed. Furthermore, by suppressing heat generation inside the tire, it is possible to prevent the inside of the tire from becoming too hot, thereby suppressing deterioration in the physical properties of the reinforcing cords containing polyamide fibers having an amide density of 14.0 or less, and as a result, it is possible to maintain the performance of the carcass layer and / or belt reinforcing layer containing the reinforcing cords containing the polyamide fibers having an amide density of 14.0 or less. Here, the loss tangent tan δ of the coating rubber can be measured using a viscoelasticity measuring device (manufactured by Rheometrics).

[0030] The coating rubber preferably has (i) a loss tangent tanδ (24°C) of 0.15 or less, more preferably 0.12 or less. When the coating rubber has a loss tangent tanδ (24°C) of 0.12 or less, heat generation inside the tire at around room temperature is further suppressed, and deterioration of the physical properties of the reinforcing cords containing polyamide fibers having an amide density of 14.0 or less is further suppressed, thereby more reliably maintaining the performance of the carcass layer and / or belt reinforcing layer containing the reinforcing cords containing polyamide fibers having an amide density of 14.0 or less. Therefore, a carcass layer and / or belt reinforcing layer using a coating rubber having a loss tangent tanδ (24°C) of 0.12 or less can further suppress deterioration of tire performance.

[0031] The coating rubber preferably has (ii) a loss tangent tanδ (60°C) of 0.10 or less, more preferably 0.07 or less. When the coating rubber has a loss tangent tanδ (60°C) of 0.07 or less, heat generation inside the tire during running is further suppressed, and the temperature inside the tire is further suppressed from rising too high. This further suppresses deterioration of the physical properties of the reinforcing cords containing polyamide fibers having an amide density of 14.0 or less, thereby more reliably maintaining the performance of the carcass layer and / or belt reinforcing layer containing the reinforcing cords containing polyamide fibers having an amide density of 14.0 or less. Therefore, a carcass layer and / or belt reinforcing layer using a coating rubber having a loss tangent tanδ (60°C) of 0.07 or less can further suppress deterioration of tire performance.

[0032] The rubber component of the rubber composition used for the coating rubber is not particularly limited, and various elastomers can be used. Examples of such elastomers include diene rubbers and hydrogenated products thereof, such as natural rubber (NR), synthetic isoprene rubber (IR), epoxidized natural rubber, styrene-butadiene rubber (SBR), butadiene rubber (BR, high cis BR, and low cis BR), nitrile rubber (NBR), hydrogenated NBR, and hydrogenated SBR, ethylene-propylene rubber (EPDM, EPM), maleic acid-modified ethylene-propylene rubber (M-EPM), butyl rubber (IIR), copolymers of isobutylene and aromatic vinyl or diene monomers, acrylic rubber (ACM), and olefinic rubbers, such as ionomers, brominated butyl rubber (Br-IIR), chlorinated butyl rubber (Cl-IIR), brominated isobutylene-paramethylstyrene copolymer (Br-IPMS), and chloroprene rubber (C Examples of rubbers that can be used include halogen-containing rubbers such as chlorosulfonated polyethylene rubber (CSM), chlorinated polyethylene rubber (CM), and maleic acid-modified chlorinated polyethylene rubber (M-CM); silicone rubbers such as methyl vinyl silicone rubber, dimethyl silicone rubber, and methyl phenyl vinyl silicone rubber; sulfur-containing rubbers such as polysulfide rubber; and fluororubbers such as vinylidene fluoride rubber, fluorine-containing vinyl ether rubber, tetrafluoroethylene-propylene rubber, fluorine-containing silicone rubber, and fluorine-containing phosphazene rubber; and thermoplastic elastomers such as styrene-based elastomers, olefin-based elastomers, ester-based elastomers, urethane-based elastomers, and polyamide-based elastomers.

[0033] The rubber components used in the coating rubber of the carcass layer and the belt reinforcing layer are preferably natural rubber (NR) or synthetic isoprene rubber (IR). The natural rubber may be modified. In the case of modified natural rubber, for example, the modified natural rubber preferably has a nitrogen content of 0.1 to 0.3 mass%. Furthermore, the modified natural rubber is preferably one from which proteins have been removed by a centrifugation process, enzyme treatment, or urea treatment. Furthermore, the modified natural rubber preferably has a phosphorus content of more than 200 ppm and not more than 900 ppm.

[0034] The rubber composition used for the coating rubber preferably contains natural rubber and styrene-butadiene rubber as rubber components, with the natural rubber content being 70 parts by mass or more per 100 parts by mass of the rubber component. The natural rubber content in the rubber composition used for the coating rubber is more preferably 70 parts by mass or more and 90 parts by mass or less per 100 parts by mass of the rubber component. Furthermore, the styrene-butadiene rubber content in the rubber composition used for the coating rubber is preferably 10 parts by mass or more and 30 parts by mass or less per 100 parts by mass of the rubber component. When natural rubber and styrene-butadiene rubber are contained as rubber components and the natural rubber content is 70 parts by mass or more per 100 parts by mass of the rubber component, the hysteresis loss of the coating rubber is further reduced, heat generation inside the tire is further suppressed, and high temperatures inside the tire can be more reliably suppressed. Therefore, a carcass layer and / or belt reinforcing layer using such a coating rubber can further suppress deterioration of tire performance.

[0035] It is preferable to use non-oil-extended styrene-butadiene rubber as the styrene-butadiene rubber. By including non-oil-extended styrene-butadiene rubber in the rubber composition, the loss tangent tan δ (24°C) of the rubber composition can be further reduced. Therefore, a carcass layer and / or belt reinforcing layer using a coating rubber containing non-oil-extended styrene-butadiene rubber can further suppress heat generation inside the tire and further suppress deterioration of tire performance.

[0036] The carbon black used in the coating rubber of the carcass layer and the belt reinforcing layer is not particularly limited, and examples thereof include GPF, FEF, HAF, ISAF, and SAF grade carbon black. These carbon blacks may be used alone or in combination of two or more. The carbon black content is preferably in the range of 40 to 80 parts by mass, more preferably 50 to 70 parts by mass, per 100 parts by mass of the rubber component.

[0037] In one embodiment, the carbon black used in the coating rubber is preferably GPF, FEF, or HAF grade carbon black. ２ SA) is 40m ２ / g or less, and ２ / g or less is more preferable, and 30m ２ / g or less. ２ SA) is 25m ２ / g or more. The content of the carbon black is preferably 30 to 60 parts by mass, more preferably 40 to 50 parts by mass, per 100 parts by mass of the rubber component. The rubber composition used for the coating rubber contains 30 to 60 parts by mass of carbon black per 100 parts by mass of the rubber component, and the nitrogen adsorption specific surface area (N ２ SA) is 40m ２ / g or less, the hysteresis loss of the coating rubber is further reduced, heat generation inside the tire is further suppressed, and the temperature inside the tire can be more reliably prevented from rising too high. Therefore, by applying such a coating rubber to a tire, it is possible to further suppress the deterioration of tire performance.

[0038] The carbon black may be recycled carbon black. Here, "recycled carbon black" refers to carbon black recovered from recycled waste raw materials. Examples of such waste include waste rubber, used tires, and waste oil. Waste rubber refers not only to waste generated from rubber products, but also to all discarded rubber, including unnecessary scraps generated during the production or repair of rubber products. Examples of scraps include buffing powder and peeled rubber. Buffing powder is fine rubber generated during the buffing process of scraping the tread portion remaining on the base tire during tire retreading, for example. Peeled rubber is a long piece of rubber, e.g., 1 to 2 cm wide, peeled from the surface of a rubber product such as a tire. Peeled rubber is generated by scraping the surface of a rubber product such as a tire using a U- or V-shaped knife like a peeler. Furthermore, waste rubber is not limited to crosslinked rubber but also includes unvulcanized rubber. Rubber products include, for example, final products such as tires and rubber hoses, as well as rubber parts or components during the manufacturing process of final products. Used tires may be tires to be retreaded, or may be tires discarded for some reason, such as tires generated during tire replacement or scrapping, or ELTs (End-of-Life Tires) that have reached the end of their service life. Waste oils are not limited to those generated during the decomposition of plastics and rubber, but also include used oils discharged from industry, such as animal and vegetable oils, lubricating oils, insulating oils, and cutting oils. Among these, waste oils that contain no non-organic components, such as those derived from silicone rubber or polyvinyl chloride, are desirable. Furthermore, waste oils containing carbon black or rubber containing carbon black are desirable. "Recycled carbon black" differs from carbon black produced directly from hydrocarbons such as petroleum, natural gas, and coal, i.e., non-recycled carbon black. Note that "used" here refers not only to waste oils discarded after actual use, but also to waste oils that were produced but discarded without actually being used.

[0039] The recycled carbon black is preferably obtained by pyrolysis of a vulcanized rubber product containing carbon black. Recycled carbon black obtained by pyrolysis of a vulcanized rubber product containing carbon black is readily available because vulcanized rubber products containing carbon black are readily available and can be easily obtained by pyrolysis. Furthermore, the recycled carbon black is preferably obtained from the solid residue produced by the pyrolysis of the vulcanized rubber product containing carbon black. When a rubber product containing carbon black is pyrolyzed, a solid residue and a volatile component (oil) are obtained, and recycled carbon black can be recovered from either of them. When recovering carbon black from the volatile component, the oil component with a specific gravity suitable for producing carbon black can be recovered and used to produce carbon black using existing carbon black production methods (e.g., JP 2015-520259 A). Unlike carbon black recovered from solid residues, this method offers advantages such as no impurities and no mixing of different grades. In addition, in the production of environmentally friendly carbon black, various options are available, including oils obtained by recovering volatile components from rubber pyrolysis, as described above, as well as vegetable oils and oils derived from waste plastics. However, edible resources such as vegetable oils are needed for other uses, such as food, and there are challenges in securing sufficient quantities, as well as the environmental impact of expanding cultivated land. Furthermore, oils derived from waste plastics are also used for other purposes, such as horizontal plastic recycling, so supply issues are also a concern. On the other hand, using volatile components (oils) produced by the pyrolysis of vulcanized rubber products, particularly tires, allows for the continued use of existing materials due to the tire industry's ongoing system of using existing materials, thereby reducing the consumption of new materials in new tire production and contributing to a reduction in the industry's environmental impact. The grade of carbon black is not particularly limited, and examples include N134, N110, N220, N234, N219, N339, N330, N326, N351, N550, and N762.

[0040] Furthermore, when the recycled carbon black is recovered from solid residue, it is more preferably carbon black that has been subjected to a surface treatment or surface modification. Examples of surface treatments or surface modifications include treatment with hydrofluoric acid, or treatment with an acid such as hydrochloric acid or sulfuric acid, or with a peroxide. Furthermore, the surface treatment or surface modification may be performed at room temperature, preferably at 70°C or higher, more preferably at 90°C or higher, and particularly preferably at 90°C or higher and 100°C or lower.

[0041] Preferably, the recycled carbon black has three or more lines 10 mm or longer when measured with a grind gauge, and the third-largest particle among the particles that produce the lines 10 mm or longer has a particle size of 20 μm or less. If the particle size of the third-largest particle is 20 μm or less, the recycled carbon black can be well dispersed in the rubber composition even when blended with the recycled carbon black, and deterioration of the durability of the rubber composition, particularly its performance after aging, can be suppressed. In the measurement using a grind gauge, a paste of the recycled carbon black can be prepared as the measurement sample in accordance with JIS K5101-1-5, and the load applied is preferably set to 0.4 to 0.5 kN and the rotation speed of the glass plate is preferably set to 90 to 110 r / min. Furthermore, for the method of evaluating the occurrence of linear scratches, it is preferable to use a sample that complies with JIS K5400 and has a range of 0 to 25 μm. A grind gauge with an upper limit of the range greater than 20 μm can be used because it can determine whether the particle size of the third largest particle is 20 μm or less. When using the gauge for other purposes (performance other than durability of the rubber composition containing recycled carbon black), the range of the grind gauge to be used can be appropriately selected depending on the purpose.

[0042] The recycled carbon black preferably has an ash content of 0.5% by mass or more and 20% by mass or less. If the ash content in the recycled carbon black exceeds 20% by mass, a tire with sufficient reinforcing properties may not be obtained. In consideration of the reinforcing properties of the tire, the ash content is preferably 10% by mass or less, and more preferably 6% by mass or less.

[0043] The rubber composition used for the coating rubber may contain, in addition to carbon black, antioxidants, sulfur, and vulcanization accelerators, zinc oxide (zinc white), stearic acid, and the like, which are commonly used in rubber products such as tires. Here, the amount of zinc white in the rubber composition is preferably more than 3 parts by mass and less than 5 parts by mass per 100 parts by mass of the rubber component. If the amount of zinc white is 5 parts by mass or more, aggregation may occur, resulting in poor dispersibility, and if it is 3 parts by mass or less, it may have an adverse effect on the vulcanization reaction.

[0044] The rubber composition used for the coating rubber preferably does not contain a polymer-derived oil component. Here, "not containing a polymer-derived oil component" means that the rubber composition does not contain an oil component that is indirectly blended into the rubber composition as a component contained in a polymer such as the rubber component. By reducing the content of polymer-derived oil components in the rubber composition used for the coating rubber to zero, the loss tangent tan δ (24°C) of the rubber composition can be further reduced. Therefore, a carcass layer and / or belt reinforcing layer using a rubber composition that does not contain a polymer-derived oil component for the coating rubber can further suppress deterioration of tire performance.

[0045] It is more preferable that the oil content in the rubber composition used for the coating rubber is 0.2% by mass or less. By making the oil content in the rubber composition used for the coating rubber 0.2% by mass or less, the loss tangent tan δ (24°C) of the rubber composition can be further reduced. Therefore, a carcass layer and / or belt reinforcing layer using a rubber composition having an oil content of 0.2% by mass or less as a coating rubber can further suppress deterioration of tire performance.

[0046] - Reinforcement cord containing polyamide fiber having an amide density of 14.0 or less - The reinforcing cord of at least one of the carcass layer and the belt reinforcing layer contains a polyamide fiber having an amide density of 14.0 or less. Compared to widely used polyamide 6,6 (PA66) fiber, polyamide fiber having an amide density of 14.0 or less has a lower amide density and fewer hydrogen bonds between amide bonds, resulting in poor thermal properties and reduced physical properties at high temperatures. In contrast, in the tire of the first embodiment of the present invention, the gauge thickness (distance) from the outer peripheral surface on the tire inner surface side of the reinforcing cord of the carcass layer located at the innermost side in the tire direction to the tire inner surface (in other words, the sum of the total thickness of the inner liner layer and the thickness of the coating rubber of the carcass layer located at the innermost side in the tire direction) is reduced to an average of 1.5 mm or less, thereby quickly dissipating heat generated inside the tire during running and preventing the inside of the tire from becoming too hot during running, thereby maintaining tire performance. In addition, in the tire of the second embodiment of the present invention, when the gauge thickness of the reinforcement cord of the belt reinforcing layer located at the outermost position in the tire radial direction from the outer peripheral surface on the tire outer surface side to the tire outer surface is measured at 100 equally spaced points, by ensuring that 80% or more of the measurement points have a gauge thickness of 6.0 mm or less (i.e., by reducing the sum of the total thickness of the tread rubber layer and the thickness of the coating rubber of the belt reinforcing layer), heat generated inside the tire during running is quickly dissipated, and the inside of the tire is prevented from becoming too hot during running, thereby maintaining tire performance. Although there is no particular lower limit for the amide density of the polyamide fiber, it is preferable that the amide density of the polyamide fiber be 10.5 or more. When the amide density of the polyamide fiber is 10.5 or more, some hydrogen bonds are formed between the amide bonds, thereby mitigating deterioration of thermal properties.

[0047] Polyamide fibers with a high bio-based content are easily used as the polyamide fibers with an amide density of 14.0 or less, and such polyamide fibers with a high bio-based content are highly effective in reducing the environmental impact. Therefore, a pneumatic tire in which a reinforcing cord containing polyamide fibers with an amide density of 14.0 or less is used in at least one of the carcass layer and the belt reinforcing layer can easily reduce the environmental impact.

[0048] The reinforcing cords of both the carcass layer and the belt reinforcing layer preferably contain polyamide fibers having an amide density of not more than 14.0. A tire in which the reinforcing cords of both the carcass layer and the belt reinforcing layer contain polyamide fibers having an amide density of not more than 14.0 facilitates the application of biomass-derived polyamide fibers to the reinforcing cords of the carcass layer and the belt reinforcing layer, facilitating a reduction in the environmental load.

[0049] A reinforcing cord containing polyamide fibers having an amide density of 14.0 or less preferably has a biomass-derived carbon content (biomass content) of 15% or more throughout the cord. A biomass content of 15% or more throughout the cord enhances the effect of reducing the environmental impact. To further reduce the environmental impact, the biomass content of the reinforcing cord is preferably 20% or more, and may be 100%.

[0050] The reinforcing cord containing the polyamide fiber having an amide density of 14.0 or less preferably contains fibers with a biomass-derived carbon content (biomass content) of 40% or more. Reinforcing cords containing fibers with a biomass content of 40% or more are more effective in reducing environmental impact. Examples of fibers (polyamide fibers) with a biomass content of 40% or more include polyamide 11 (PA11) fiber, polyamide 4,10 (PA410) fiber, polyamide 6,10 (PA610) fiber, and polyamide 10,10 (PA1010). The polyamides used as the raw material for these polyamide fibers can be synthesized from biomass-derived components. Here, biomass-derived components refer to components derived from biological resources such as plant resources, animal resources, and microbial resources.

[0051] Polyamide 11 (PA11) is obtained by polymerization of aminoundecanoic acid, which is obtained from plant resources such as castor beans. Polyamide 4,10 (PA410) is obtained by condensation polymerization of tetramethylenediamine (carbon number 4) and sebacic acid (carbon number 10), which is obtained from plant resources such as sugarcane. Polyamide 6,10 (PA610) is obtained by condensation polymerization of hexamethylenediamine (carbon number 6) and sebacic acid (carbon number 10), which is obtained from plant resources such as castor beans. Polyamide 10,10 (PA1010) is obtained by the condensation polymerization reaction of decamethylenediamine (C10) and sebacic acid (C10). Decamethylenediamine and sebacic acid are obtained from plant resources such as castor beans. For example, tetramethylenediamine, also known as "putrescine," can be obtained by fermenting sugarcane to produce glutamic acid, biochemically producing ornithine from the glutamic acid, and decarboxylating the resulting ornithine. Sebacic acid can be obtained by mechanically pressing castor beans to obtain castor oil, methanolyzing the castor oil to obtain methyl ricinoleate, and then saponifying the methyl ricinoleate.

[0052] The reinforcing cord containing the polyamide fiber having an amide density of 14.0 or less preferably contains the fiber whose bio-based content is 100% (i.e., entirely derived from biomass). By including the fiber whose bio-based content is 100%, the effect of reducing the environmental load is further enhanced. Examples of the fiber whose bio-based content is 100% include polyamide 11 (PA11) fiber, polyamide 4,10 (PA410) fiber, and polyamide 10,10 (PA1010) fiber.

[0053] Examples of polyamide fibers having an amide density of 14.0 or less include polyamide 4,10 (PA410) fibers, polyamide 6,10 (PA610) fibers, polyamide 9,T (PA9T) fibers, polyamide 10,10 (PA1010) fibers, and polyamide 11 (PA11) fibers. Among these, polyamide 4,10 (PA410) fibers are preferred. Polyamide 4,10 fibers with a 100% bio-based content can be used, and such 100% bio-based polyamide 4,10 fibers are highly effective in reducing environmental impact. Therefore, a pneumatic tire in which a reinforcing cord containing polyamide 4,10 fibers is applied to at least one of the carcass layer and the belt reinforcing layer can easily reduce environmental impact.

[0054] The reinforcing cord may contain organic fibers other than polyamide fibers having an amide density of 14.0 or less. Here, the raw material of the organic fibers other than polyamide fibers having an amide density of 14.0 or less is not particularly limited, and may be derived from synthetic products, biological resources such as plant resources, animal resources, or microbial resources, mechanically recycled by crushing, melting, and re-spinning a resin product, or chemically recycled by depolymerizing and repolymerizing a resin product.

[0055] The material of the organic fiber is not particularly limited, and examples thereof include polyesters such as polyethylene terephthalate (PET), polyethylene naphthalate (PEN), and polyethylene furan dicarboxylate (PEF); polyamides such as 6-nylon (registered trademark), 6,6-nylon (registered trademark), 4,6-nylon (registered trademark), and aramid; and celluloses such as rayon and lyocell.

[0056] Examples of the polyethylene terephthalate (PET) include polyethylene terephthalate obtained by mechanically or chemically recycling PET products, clothing, and the like.

[0057] Examples of the polyamide include polyamides derived from biological resources, such as polyamide 4 (PA4), polyamide 4,4 (PA44), polyamide 5,4 (PA54), polyamide 4,6 (PA46), polyamide 5,6 (PA56), polyamide 6 (also referred to as PA6:6-nylon (registered trademark)), and polyamide 6,6 (also referred to as PA66:6,6-nylon (registered trademark)).

[0058] The reinforcing cord containing the polyamide fiber having an amide density of 14.0 or less is preferably a cord obtained by twisting together the fiber having a bio content of 40% or more and aramid fiber. Such a reinforcing cord has rigidity and excellent thermal properties due to the aramid fiber, and is also effective in reducing the environmental load due to the bio content of the fiber being 40% or more.

[0059] The reinforcing cord containing polyamide fiber having an amide density of 14.0 or less is preferably a cord twisted together with polyamide 4,10 fiber and aramid fiber. Such a reinforcing cord has rigidity and excellent thermal properties due to the aramid fiber, and is also effective in reducing the environmental load due to the polyamide 4,10 fiber, which can be used with a 100% bio-based content.

[0060] The reinforcing cord containing polyamide fibers having an amide density of 14.0 or less is also preferably a cord formed by twisting two to four fibers together. A reinforcing cord formed by twisting two to four fibers together can achieve a lightweight tire while ensuring sufficient rigidity as a tire reinforcing material. From the same viewpoint, a cord formed by twisting two fibers together is preferred.

[0061] The reinforcing cord containing the polyamide fiber having an amide density of 14.0 or less is preferably a cord twisted together of two aramid fibers and one polyamide 4,10 fiber. Such a reinforcing cord has rigidity and excellent thermal properties due to the two aramid fibers, and is also effective in reducing the environmental load due to the polyamide 4,10 fiber, which can be used with a 100% bio-based content.

[0062] The reinforcing cord containing the polyamide fiber having an amide density of 14.0 or less is preferably made exclusively of polyamide fiber having a biomass-derived carbon content (biomass content) of 15% or more. By making the reinforcing cord exclusively of polyamide fiber having a biomass content of 15% or more, the effect of reducing the environmental load is enhanced.

[0063] The reinforcing cord may have a single twist structure or a twisted structure (such as a double twist structure). In the case of a single twist structure, for example, raw yarns are pulled together and twisted in one direction to obtain a twisted cord. Here, the number of twists is preferably in the range of 4 to 20 times per 10 cm. If the number of twists in a single twist structure exceeds 20 times per 10 cm, the strength of the twisted cord may decrease, and if it is less than 4 times per 10 cm, the twisted cord may not have sufficient fatigue resistance. In the case of a double twist structure, for example, raw yarns are first twisted, and then multiple such twists are combined and then second twisted in the opposite direction to obtain a twisted cord. Here, the number of first twists is preferably in the range of 10 to 60 times per 10 cm, and the number of second twists is preferably in the range of 10 to 60 times per 10 cm. If the number of first twists exceeds 60 times / 10 cm, the strength of the twisted cord may decrease, and if it is less than 10 times / 10 cm, the twisted cord may not have sufficient fatigue resistance.If the number of final twists exceeds 60 times / 10 cm, the strength of the twisted cord may decrease, and if it is less than 10 times / 10 cm, the twisted cord may not have sufficient fatigue resistance.

[0064] The reinforcing cord containing the polyamide fiber having an amide density of 14.0 or less preferably has a heat shrinkage rate of 12.0% or less. When the reinforcing cord has a heat shrinkage rate of 12.0% or less, deterioration of physical properties (particularly modulus of elasticity and strength) at high temperatures can be suppressed. The reinforcing cord more preferably has a heat shrinkage rate of 9.0% or less. When the reinforcing cord has a heat shrinkage rate of 9.0% or less, uniformity is improved, particularly during high-speed running.

[0065] The total fineness of the reinforcing cord containing the polyamide fiber having an amide density of 14.0 or less is preferably in the range of 1000 to 6000 dtex. If the total fineness of the reinforcing cord is less than 1000 dtex, sufficient strength as a tire reinforcing cord may not be obtained, and if it exceeds 6000 dtex, the treat becomes thick, increasing the tire weight.

[0066] The breaking strength of the reinforcement cord containing the polyamide fiber having an amide density of 14.0 or less is preferably 6.0 cN / dtex or more. The breaking strength of the reinforcement cord is preferably 180 N or more. Here, the breaking strength is measured at room temperature (23°C) in accordance with ASTM D855M. A sufficient reinforcing effect can be obtained when the breaking strength of the reinforcement cord is 6.0 cN / dtex or more, or 180 N or more.

[0067] The reinforcing cord containing the polyamide fiber having an amide density of 14.0 or less preferably has a breaking elongation (elongation at break) of 8.0% or more. Here, the breaking elongation is measured at room temperature (23°C) in accordance with ASTM D855M. When the breaking elongation of the reinforcing cord is 8.0% or more, a sufficient reinforcing effect can be obtained.

[0068] The moisture regain of the reinforcing cord containing the polyamide fiber having an amide density of 14.0 or less is preferably 3.0% or less. Here, the moisture regain is measured in accordance with JIS L 1013. If the moisture regain of the reinforcing cord exceeds 3.0%, the physical properties will be deteriorated and a sufficient reinforcing effect will not be obtained.

[0069] -Other Reinforcing Cords- When one of the carcass layer and the belt reinforcing layer includes a reinforcing cord containing a polyamide fiber having an amide density of 14.0 or less, the other of the carcass layer and the belt reinforcing layer does not need to include a reinforcing cord containing a polyamide fiber having an amide density of 14.0 or less. In this case, the reinforcing cord can be a reinforcing cord containing any organic fiber, and in addition to a polyamide fiber cord, a polyester fiber cord or the like can also be used.

[0070] -Adhesive Composition- The reinforcing cords used in the carcass layer and the belt reinforcing layer are preferably treated with an adhesive composition.

[0071] Examples of the adhesive composition include an adhesive composition containing a thermoplastic polymer (A) having at least one crosslinkable functional group as a pendant group and substantially no addition-reactive carbon-carbon double bonds in its main chain structure, a heat-reactive aqueous urethane resin (B), and an epoxy compound (C), and optionally further containing a rubber latex (D). Treating the reinforcing cord with such an adhesive composition can improve the adhesion between the reinforcing cord and elastomer (coating rubber) at high temperatures.

[0072] Conventionally, adhesive treatment of organic fiber cords has been performed using a so-called two-bath process, in which epoxy or isocyanate is applied to the cord surface, followed by treatment with a resin (hereinafter referred to as RFL resin) composed of a mixture of resorcinol, formaldehyde, and latex. However, this method can result in the resin used in the first bath becoming very hard, increasing strain input to the organic fiber cord and reducing cord fatigue resistance. Furthermore, while such RFL resins can exhibit sufficient cord-to-elastomer adhesion at room temperature, they can experience a significant decrease in adhesion at temperatures above 130°C. In contrast, by using a one-bath mixture (adhesive composition) containing a thermoplastic polymer (A) having at least one crosslinkable functional group as a pendant group and substantially free of addition-reactive carbon-carbon double bonds in its main chain structure, a thermally reactive aqueous urethane resin (B), and an epoxy compound (C), sufficient adhesion to the elastomer (coating rubber) can be ensured without curing the reinforcing cord, even at temperatures above 180°C.

[0073] The main chain of the thermoplastic polymer (A) mainly has a linear structure, and the main chain is preferably, for example, an ethylenic addition polymer such as an acrylic polymer, a vinyl acetate polymer, or a vinyl acetate-ethylene polymer; a urethane high molecular weight polymer; etc. However, the thermoplastic polymer (A) is not limited to the above-mentioned ethylenic addition polymer and urethane high molecular weight polymer, as long as it has the function of suppressing resin fluidity at high temperatures and ensuring the breaking strength of the resin by crosslinking the functional groups of the pendant groups.

[0074] The functional group of the pendant group of the thermoplastic polymer (A) is preferably an oxazolidine group, a bismaleimide group, a (blocked) isocyanate group, an aziridine group, a carbodiimide group, a hydrazino group, an epoxy group, an epithio group, or the like.

[0075] In addition, with respect to the above-mentioned thermoplastic polymer (A), heat-reactive aqueous urethane resin (B), epoxy compound (C), and rubber latex (D), those described in Japanese Patent Application No. 2023-040157 and those described in Japanese Patent Application No. 2023-030762 can be used.

[0076] In the adhesive treatment of the reinforcing cord, it is preferable to use a three-type mixed liquid (adhesive composition) of the thermoplastic polymer (A), the heat-reactive aqueous urethane resin (B), and the epoxy compound (C) as a one-bath treatment liquid, and to use a normal RFL resin liquid as a two-bath treatment liquid. In addition, in the adhesive treatment, it is also possible to treat with only one bath using a mixed liquid (adhesive composition) of the thermoplastic polymer (A), the heat-reactive aqueous urethane resin (B), the epoxy compound (C), and the rubber latex (D).

[0077] In the adhesive composition, the proportion (dry mass ratio) of the thermoplastic polymer (A) is preferably 2 to 75%, the proportion (dry mass ratio) of the heat-reactive aqueous urethane resin (B) is preferably 15 to 87%, the proportion (dry mass ratio) of the epoxy compound (C) is preferably 11 to 70%, and the proportion (dry mass ratio) of the rubber latex (D) is preferably 20% or less.

[0078] On the other hand, from the viewpoint of environmental protection, it is preferable to use a dip treatment liquid that does not contain resorcinol or formalin as the adhesive composition for the reinforcing cord. Examples of such dip treatment liquids include a composition containing (a) a rubber latex having an unsaturated diene and (b) one or more compounds selected from a compound having a polyether skeleton structure and an amine functional group, a compound having an acrylamide structure, a polypeptide, a polylysine, and a carbodiimide. Examples of such dip treatment liquids include a composition containing, in addition to the rubber latex (a) having an unsaturated diene and the compound (b), one or more compounds selected from (c) an aqueous compound having a (thermally dissociable blocked) isocyanate group, a polyphenol (d), and a polyvalent metal salt (e).

[0079] Other examples of the dipping treatment liquid that does not contain resorcinol or formalin include a composition containing polyphenols (I) and aldehydes (II). Such a composition may further contain at least one of an isocyanate compound (III) and a rubber latex (IV) in addition to the polyphenols (I) and aldehydes (II).

[0080] By including polyphenols (I) and aldehydes (II) in the adhesive composition used to treat (coat) the reinforcing cord with an adhesive, good adhesive properties can be achieved even when resorcinol is not used in consideration of the environmental impact.

[0081] --Polyphenols (I)-- The adhesive composition contains polyphenols (I) as a resin component, thereby improving adhesion to the reinforcing cord. The polyphenols (I) are typically water-soluble polyphenols, and are not particularly limited as long as they are polyphenols other than resorcinol (resorcinol). The number of aromatic rings or the number of hydroxyl groups in the polyphenols (I) can be appropriately selected.

[0082] From the viewpoint of realizing better adhesive properties, the polyphenols (I) preferably have two or more hydroxyl groups, and more preferably three or more hydroxyl groups. When the polyphenols have three or more hydroxyl groups, the polyphenol or polyphenol condensate is soluble in the adhesive composition (dip treatment liquid) containing water. This allows the polyphenols to be uniformly distributed in the adhesive composition, thereby realizing better adhesive properties. Furthermore, when the polyphenols (I) are polyphenols containing multiple (two or more) aromatic rings, each of the aromatic rings has two or three hydroxyl groups at the ortho, meta, or para positions.

[0083] As the polyphenols (I), for example, those described as polyphenol compounds in WO 2022 / 130879 can be used. These polyphenols (I) may be used alone or in combination of two or more.

[0084] --Aldehydes (II)-- The adhesive composition contains aldehydes (II) as a resin component in addition to the polyphenols (I) described above, thereby achieving high adhesiveness together with the polyphenols (I). The aldehydes (II) are not particularly limited and can be appropriately selected depending on the required performance. In this specification, the aldehydes (II) also include derivatives of aldehydes that are generated from aldehydes.

[0085] Examples of the aldehydes (II) include monoaldehydes such as formaldehyde, acetaldehyde, butylaldehyde, acrolein, propionaldehyde, chloral, butylaldehyde, caproaldehyde, and allylaldehyde, and aliphatic dialdehydes such as glyoxal, malonaldehyde, succinaldehyde, glutaraldehyde, and adipaldehyde, aldehydes having an aromatic ring, and dialdehyde starch. These aldehydes (II) may be used singly or in combination of two or more.

[0086] The aldehydes (II) are preferably aldehydes having an aromatic ring or contain aldehydes having an aromatic ring, because this allows for better adhesiveness to be obtained. Furthermore, the aldehydes (II) preferably do not contain formaldehyde. Here, "does not contain formaldehyde" means, for example, that the formaldehyde content of the total mass of the aldehydes is less than 0.5 mass%.

[0087] In the adhesive composition, polyphenols (I) and aldehydes (II) are in a condensed state, and the mass ratio of the polyphenols to the aldehydes having an aromatic ring (content of aldehydes having an aromatic ring / content of polyphenols) is preferably 0.1 or more and 3 or less. In this case, the hardness and adhesive properties of the resin, which is the product of the condensation reaction between the polyphenols and the aldehydes having an aromatic ring, are more suitable. From the same viewpoint, the mass ratio of the polyphenols to the aldehydes having an aromatic ring (content of aldehydes having an aromatic ring / content of polyphenols) in the adhesive composition is more preferably 0.25 or more and more preferably 2.5 or less. Note that the above mass ratio is the mass of the dry product (solid content ratio).

[0088] The total content of polyphenols (I) and aldehydes (II) in the adhesive composition is preferably 3 to 30% by mass. This is because better adhesion can be ensured without deteriorating workability, etc. From the same viewpoint, the total content of polyphenols (I) and aldehydes (II) in the adhesive composition is more preferably 5% by mass or more, and more preferably 25% by mass or less. The above total content is the mass of the dry product (solid content ratio).

[0089] --Isocyanate Compound (III)--The adhesive composition preferably further contains an isocyanate compound (III) in addition to the polyphenols (I) and aldehydes (II) described above. In this case, the adhesive composition can further enhance the adhesiveness due to a synergistic effect with the polyphenols (I) and the aldehydes (II).

[0090] Here, the isocyanate compound (III) is a compound that has the effect of promoting adhesion of the adhesive composition to a resin material (e.g., a phenol / aldehyde resin obtained by condensing polyphenols (I) and aldehydes (II)) that is the adherend, and is a compound that has an isocyanate group as a polar functional group. These isocyanate compounds (III) may be used alone or in combination of two or more.

[0091] The isocyanate compound (III) is not particularly limited, but from the viewpoint of further improving adhesion, it preferably contains a (blocked) isocyanate group-containing aromatic compound. When the adhesive composition contains a (blocked) isocyanate group-containing aromatic compound, the (blocked) isocyanate group-containing aromatic compound is distributed in a position near the interface between the reinforcing cord and the adhesive composition, resulting in a further adhesion-promoting effect, and this effect can further improve the adhesion of the adhesive composition to the reinforcing cord.

[0092] As the (blocked) isocyanate group-containing aromatic compound, those described in Japanese Patent Application No. 2023-040157 and Japanese Patent Application No. 2023-030762 can be used.

[0093] The content of the isocyanate compound (III) in the adhesive composition is not particularly limited, but from the viewpoint of more reliably ensuring excellent adhesion, it is preferably 5 to 65% by mass. From the same viewpoint, the content of the isocyanate compound (III) in the adhesive composition is more preferably 10% by mass or more, and more preferably 45% by mass or less. The above content is the mass of the dry product (solid content ratio).

[0094] --Rubber Latex (IV)-- The adhesive composition may further contain substantially rubber latex (IV) in addition to the polyphenols (I), aldehydes (II), and isocyanate compound (III) described above, which allows the adhesive composition to have even greater adhesion to rubber members.

[0095] Here, the rubber latex (IV) is not particularly limited, and examples thereof include natural rubber (NR), as well as synthetic rubbers such as polyisoprene rubber (IR), styrene-butadiene copolymer rubber (SBR), polybutadiene rubber (BR), ethylene-propylene-diene rubber (EPDM), chloroprene rubber (CR), halogenated butyl rubber, acrylonitrile-butadiene rubber (NBR), and vinylpyridine-styrene-butadiene copolymer rubber (Vp). These rubber latexes (IV) may be used alone or in combination of two or more.

[0096] When preparing the adhesive composition containing the rubber latex (IV), it is preferable to mix the rubber latex (IV) with the phenol (I) and the aldehyde (II) before compounding the isocyanate compound (III).

[0097] The content of the rubber latex (IV) in the adhesive composition is preferably 20% by mass or more, more preferably 25% by mass or more, and is preferably 70% by mass or less, more preferably 60% by mass or less.

[0098] The method for producing the adhesive composition is not particularly limited, and examples thereof include a method of mixing raw materials such as polyphenols (I), aldehydes (II), and rubber latex (IV) and aging the mixture, or a method of mixing polyphenols (I) and aldehydes (II) and aging the mixture, and then adding rubber latex (IV) and aging the mixture. When an isocyanate compound (III) is contained in the raw materials, the method for producing the adhesive composition may also be a method of adding rubber latex (IV), aging the mixture, and then adding the isocyanate compound (III).

[0099] (Belt Layer) The pneumatic tires of the first and second embodiments of the present invention include a belt layer on the tire radially outer side of the crown portion of the carcass layer. The number of belt layers is not particularly limited and may be one, two, or three or more. The belt layer is typically formed by coating reinforcing cords that extend at an angle (for example, at an angle of 15 to 40°) with a coating rubber with respect to the tire equatorial plane, and preferably by coating steel cords with a coating rubber. Furthermore, typically, two or more belt layers are laminated such that the reinforcing cords constituting the belt layers cross each other with the tire equatorial plane in between, and are disposed on the tire radially outer side of the crown portion of the carcass layer.

[0100] -Coating Rubber- As the coating rubber of the belt layer, a rubber composition can be used in which a rubber component such as natural rubber or synthetic rubber is blended with a filler such as carbon black, an antioxidant, an adhesion promoter such as a cobalt compound containing a cobalt salt, a vulcanizing agent such as sulfur, a vulcanization accelerator, etc.

[0101] The rubber component used for the coating rubber of the belt layer is preferably natural rubber (NR) or synthetic isoprene rubber (IR). The natural rubber may be modified. In the case of modified natural rubber, for example, the modified natural rubber preferably has a nitrogen content of 0.1 to 0.3 mass%. Furthermore, the modified natural rubber is preferably one from which proteins have been removed by a centrifugation process, enzyme treatment, or urea treatment. Furthermore, the modified natural rubber preferably has a phosphorus content of more than 200 ppm and not more than 900 ppm.

[0102] The carbon black used in the coating rubber of the belt layer is not particularly limited, and examples thereof include GPF, FEF, HAF, ISAF, and SAF grade carbon black. These carbon blacks may be used alone or in combination. The carbon black content is preferably 40 to 80 parts by mass, more preferably 50 to 70 parts by mass, per 100 parts by mass of the rubber component. The carbon black may also be recycled carbon black. Here, "recycled carbon black" refers to carbon black obtained by recovering recycled waste from raw materials, and is the same as the "recycled carbon black" described above as an example of the carbon black used in the coating rubber of the carcass layer and belt reinforcing layer. Examples of the recycled waste include rubber products (particularly vulcanized rubber products) containing carbon black, such as used rubber and used tires, and waste oil. Further details of the waste are the same as those described above. "Recycled carbon black" is different from carbon black that is directly manufactured using hydrocarbons such as petroleum, natural gas, and coal as raw materials, i.e., non-recycled carbon black. Note that "used" here does not only include carbon black that has been discarded after actual use, but also carbon black that has been manufactured but discarded without actually being used.

[0103] The recycled carbon black for the coating rubber of the belt layer is also preferably obtained by pyrolysis of a vulcanized rubber product containing carbon black. The recycled carbon black obtained by pyrolysis of a vulcanized rubber product containing carbon black is easily available because there are a large number of vulcanized rubber products containing carbon black and it can be easily obtained by pyrolysis. Details of the pyrolysis of vulcanized rubber products containing carbon black are the same as those described above.

[0104] Furthermore, when the recycled carbon black for the coating rubber of the belt layer is recovered from solid residue, it is preferably carbon black that has been subjected to a surface treatment or surface modification. Examples of the surface treatment or surface modification include treatment with hydrofluoric acid, or treatment with an acid such as hydrochloric acid or sulfuric acid, or with a peroxide. The surface treatment or surface modification may be performed at room temperature, preferably at 70°C or higher, more preferably at 90°C or higher, and particularly preferably at 90°C or higher and 100°C or lower.

[0105] The recycled carbon black for the coating rubber of the belt layer also preferably has three or more lines of 10 mm or more in length when measured with a grind gauge, and the particle size of the third-largest particle among the particles that produce the lines of 10 mm or more in length is 20 μm or less. If the particle size of the third-largest particle is 20 μm or less, even when recycled carbon black is blended, the recycled carbon black has good dispersibility in the rubber composition, and the durability of the rubber composition, particularly the deterioration of performance after aging, can be suppressed. Details of the grind gauge measurement are the same as above.

[0106] The recycled carbon black for the coating rubber of the belt layer also preferably has an ash content of 0.5% by mass or more and 20% by mass or less. If the ash content in the recycled carbon black exceeds 20% by mass, a tire with sufficient reinforcement may not be obtained. In consideration of the reinforcement of the tire, the ash content is preferably 10% by mass or less, and more preferably 6% by mass or less.

[0107] -Reinforcement Cord- The reinforcing cord used in the belt layer is not particularly limited, but is preferably a steel cord. The structure of the steel cord is not particularly limited. However, from the viewpoint of effectively achieving both improved tire durability and low rolling resistance, the steel cord may have a 1×N structure (N is an integer of 2 or more) formed by twisting together N filaments, an M+N structure in which N sheath filaments (N is an integer greater than 1) are twisted spirally around M core filaments (here, M is an integer of 1 or more) (here, the core filaments may be twisted together or may be bundled together without twisting), or a multi-twist structure in which a plurality of the 1×N structure or M+N structure are twisted together. Furthermore, the cord is preferably a monofilament that is pulled parallel to one another without being twisted together. In addition, in tires, steel cords can be used, for example, as belt cords in belt layers (usually arranged in the tread portion), as well as belt reinforcing layer cords in belt reinforcing layers; carcass cords; reinforcing cords in wire chafers (usually arranged on the outer side of the folded-up portion of the carcass in the tire width direction); bead cords in bead cores (usually arranged in the bead portion); etc.

[0108] The filaments constituting the above-mentioned steel cord preferably satisfy the following formula: 4000-2000X≦Y≦4500-2000X, where X (mm) is the diameter of the filament and Y (MPa) is the tensile strength of the filament. By using filaments that satisfy the above formula, the strength of the steel cord can be improved, and the cut resistance of the tire can be improved. Here, the tensile strength of the filament is determined in accordance with the provisions of ISO 17832:2009.

[0109] From the viewpoint of fatigue resistance, the hardness of the surface layer of the filament constituting the above-mentioned steel cord is preferably 90 to 110%, and particularly preferably 100%, of the hardness of the inner layer. The hardness can be measured, for example, by Vickers hardness. The surface layer of the filament refers to the layer extending from the outermost surface to a depth of 0.01 mm, and the inner layer refers to the layer extending further inside. The hardness can be measured in a region 0.005 mm deep from the outermost surface for the surface layer, and in a region 0.04 mm deep for the inner layer.

[0110] The steel filaments constituting the above-mentioned steel cord may be steel filaments derived from recycled iron.

[0111] The raw material of the recycled iron is not particularly limited, and examples thereof include scrap iron, steel cords extracted from tires, etc. ２ From the viewpoint of reducing emissions, recycled iron obtained from an electric furnace (electric furnace steelmaking method) is preferred.

[0112] The steel filaments derived from recycled iron preferably have an N (nitrogen) content of 60 ppm to 200 ppm by mass, preferably 60 ppm to 89 ppm by mass, a C (carbon) content of 0.7 to 1.0% by mass, a Cu (copper) content of 0.01 to 0.4% by mass, and a Cr (chromium) content of 0.05 to 0.3% by mass. Such steel filaments can be produced using, as a raw material, general recycled iron having an N (nitrogen) content of 60 ppm to 200 ppm by mass, a C (carbon) content of 0.7 to 1.0% by mass, a Cu (copper) content of 0.01 to 0.4% by mass, and a Cr (chromium) content of 0.05 to 0.3% by mass. Such steel filaments do not require advanced refining during production, and therefore the production process is not complicated. Furthermore, such steel filaments can reduce energy consumption during production and also reduce CO ２ This is also preferable from an environmental perspective, as it reduces emissions.

[0113] The steel filaments derived from recycled iron preferably contain iron as the main component and have an Fe (iron) element content of 98% by mass or more.

[0114] (Inner liner layer) The pneumatic tire of the first embodiment of the present invention includes an inner liner layer adjacent to the tire inner surface side of the carcass layer. Furthermore, the pneumatic tire of the second embodiment of the present invention preferably includes an inner liner layer adjacent to the tire inner surface side of the carcass layer. The number of inner liner layers is not particularly limited, and may be one layer or two or more layers. The inner liner layer has the function of maintaining the internal pressure of the pneumatic tire, and a rubber with low air permeability is used for the inner liner layer. Examples of such a rubber with low air permeability include a rubber composition containing a rubber component such as butyl rubber or halogenated butyl rubber, a filler such as carbon black, an antioxidant, a vulcanizing agent such as sulfur, a vulcanization accelerator, and the like.

[0115]

[0023] Next, an example of a pneumatic tire according to a first embodiment of the present invention will be described in detail with reference to the drawings. Fig. 1 is a cross-sectional view of the example of a pneumatic tire according to the first embodiment of the present invention (more specifically, a cross-sectional view of a tire cross section perpendicular to the tire circumferential direction).

[0116] The tire 100 shown in FIG. 1 has a pair of bead portions 10, a pair of sidewall portions 20, and a tread portion 30 continuous with both sidewall portions 20, and is equipped with: a carcass layer 50 extending in a toroidal shape between bead cores 40 embedded in the pair of bead portions 10; two belt layers 60A, 60B arranged on the tire radial outside of the crown portion of the carcass layer 50; a belt reinforcing layer (also referred to as a "cap layer") 70A arranged on the tire radial outside of the belt layers 60A, 60B so as to cover the entire belt layers 60A, 60B; a pair of belt reinforcing layers (also referred to as "layer layers") 70B arranged so as to cover only both end portions of the belt reinforcing layer 70A; and an inner liner layer 80 arranged adjacent to the carcass layer 50 on the tire inner surface side.

[0117] In the tire 100 shown in Fig. 1 , the carcass layer 50 is a single layer, but in the pneumatic tire of the first embodiment of the present invention, the number of carcass layers may be two or more. In addition, in the tire 100 shown in Fig. 1 , the carcass layer 50 is composed of a main body portion extending in a toroidal shape between a pair of bead cores 40 each embedded in the bead portion 10, and a folded-up portion wound up radially outward around each bead core 40 from the inner side toward the outer side in the tire width direction. However, in the pneumatic tire of the first embodiment of the present invention, the shape and structure of the carcass layer 50 are not limited to this. Here, the carcass layer 50 is preferably formed by coating a plurality of reinforcing cords that extend in a direction approximately perpendicular to the tire circumferential direction (for example, extending at an angle of 70 to 90 degrees) with a coating rubber; that is, the carcass layer 50 is preferably a radial carcass. The reinforcing cords of the carcass layer 50 are preferably the reinforcing cords containing the polyamide fibers described above, but when the reinforcing cords containing the polyamide fibers described above are applied to the belt reinforcing layers 70A, 70B, other organic fiber cords or steel cords may be used. Examples of the other organic fiber cords include polyethylene terephthalate cords and rayon cords.

[0118] 1 has two belt layers 60A, 60B, but the number of belt layers in the pneumatic tire of the first embodiment of the present invention may be one or three or more. In the tire 100 shown in Fig. 1, each of the belt layers 60A, 60B is usually formed by coating reinforcing cords that extend at an angle inclined with respect to the tire equatorial plane (for example, at an angle of 15 to 40 degrees) with a coating rubber, and preferably by coating steel cords with a coating rubber, and further, the two belt layers 60A, 60B are layered such that the reinforcing cords constituting the belt layers 60A, 60B intersect with each other with the tire equatorial plane in between.

[0119] In the tire 100 shown in FIG. 1 , the belt reinforcing layers 70A, 70B are formed by coating reinforcing cords with a coating rubber, the reinforcing cords being arranged substantially parallel to the tire circumferential direction (e.g., at an angle of 0 to 5 degrees relative to the tire circumferential direction). The belt reinforcing layers 70A, 70B are formed by continuously spirally winding narrow strips of reinforcing cords coated with a coating rubber in the tire circumferential direction. In this case, the absence of joints in the tire circumferential direction improves tire uniformity, and the absence of joints also prevents strain concentration at the joints. The reinforcing cords in the belt reinforcing layers 70A, 70B are preferably reinforcing cords containing the polyamide fibers described above. However, when the reinforcing cords containing the polyamide fibers described above are used in the carcass layer 50, other organic fiber cords may also be used. Examples of other organic fiber cords include polyethylene terephthalate cords and rayon cords. 1 includes a belt reinforcing layer 70A and a belt reinforcing layer 70B, but a tire in which either the belt reinforcing layer 70A or the belt reinforcing layer 70B is omitted is also an example of a pneumatic tire according to the first embodiment of the present invention. In addition, in the tire 100 shown in FIG. 1, the belt reinforcing layer (cap layer) 70A and the belt reinforcing layer (layer layer) 70B each comprise one layer, but may comprise two or more layers.

[0120] 1, the tire 100 has one inner liner layer 80, but the number of inner liner layers may be two or more in the pneumatic tire of the first embodiment of the present invention. The inner liner layer 80 has the function of maintaining the internal pressure of the tire, and a rubber with low air permeability is used for the inner liner layer 80.

[0121] Figure 2 is an enlarged view of the area surrounded by dashed line II in the tread portion 30 of the tire 100 shown in Figure 1. In Figure 2, the carcass layer 50 and the belt reinforcing layer 70A include reinforcement cords 50-1, 70A-1. Here, the carcass layer 50 is composed of a reinforcement cord 50-1 and a coating rubber 50-2 that coats the reinforcement cord 50-1. Similarly, the belt reinforcing layer 70A is composed of a reinforcement cord 70A-1 and a coating rubber 70A-2 that coats the reinforcement cord 70A-1. Furthermore, at least one of the reinforcement cord 50-1 of the carcass layer 50 and the reinforcement cord 70A-1 of the belt reinforcing layer 70A contains the above-mentioned polyamide fiber having an amide density of 14.0 or less. In addition, a tire in which neither the reinforcing cord 50-1 of the carcass layer 50 nor the reinforcing cord 70A-1 of the belt reinforcing layer 70A contains polyamide fiber having an amide density of 14.0 or less, and the reinforcing cord of the belt reinforcing layer (layer) 70B not shown in Figure 2 contains polyamide fiber having an amide density of 14.0 or less, is also an example of a pneumatic tire of the first embodiment of the present invention.

[0122] 1 and 2, the tire width direction D of the tire cross section perpendicular to the tire circumferential direction Ｗ In the region R where the belt reinforcing layers 70A and 70B are arranged, Ｒ When the gauge thickness (distance) A from the outer peripheral surface on the tire inner surface side of the reinforcement cord 50-1 of the innermost carcass layer 50 to the tire inner surface is measured at 100 equally spaced points, the average of the gauge thickness A is 1.5 mm or less. In Figure 2, the gauge thickness A from the outer peripheral surface on the tire inner surface side of the reinforcement cord 50-1 of the carcass layer 50 to the tire inner surface is the total thickness B of the inner liner layer 80 and the tire radial direction D ＲThe gauge thickness A corresponds to the sum of the thickness C of the coating rubber 50-2 of the carcass layer 50 located at the innermost position (i.e., A = B + C). By reducing the average gauge thickness A to 1.5 mm or less, as described above, heat generated inside the tire during running is quickly dissipated, preventing the inside of the tire from becoming too hot during running. By preventing the inside of the tire from becoming too hot during running, deterioration of the physical properties of the reinforcing cord containing polyamide fiber having an amide density of 14.0 or less is suppressed, thereby maintaining tire performance. Furthermore, the average gauge thickness A (i.e., the sum of the total thickness B of the inner liner layer 80 and the thickness C of the coating rubber 50-2 of the carcass layer 50 located at the innermost position in the tire radial direction) is preferably 1.0 mm or less. A pneumatic tire having an average gauge thickness A of 1.0 mm or less is suitable as a racing tire.

[0123] In the pneumatic tire according to the first embodiment of the present invention, the reinforcing cords of both the carcass layer 50 and the belt reinforcing layers 70A, 70B preferably contain polyamide fibers having an amide density of not more than 14.0. When the reinforcing cords of both the carcass layer 50 and the belt reinforcing layers 70A, 70B contain polyamide fibers having an amide density of not more than 14.0, it becomes easy to apply biomass-derived polyamide fibers to the reinforcing cords of the carcass layer 50 and the belt reinforcing layers 70A, 70B, and it becomes easy to reduce the environmental load.

[0124] In the pneumatic tire of the first embodiment of the present invention, it is preferable that the total thickness C of the inner liner layer 80 is 1.0 mm or less. When the total thickness C of the inner liner layer 80 is 1.0 mm or less, Ｒ By reducing the average gauge thickness A from the outer peripheral surface on the tire inner surface side of the reinforcement cord 50-1 of the innermost carcass layer 50 to the tire inner surface, heat generated inside the tire during running is dissipated more quickly, further suppressing the inside of the tire from becoming too hot during running, and further suppressing the deterioration of the physical properties of the reinforcement cord containing polyamide fiber with an amide density of 14.0 or less, thereby more reliably maintaining tire performance.

[0125] Next, an example of a pneumatic tire according to a second embodiment of the present invention will be described in detail with reference to the drawings. Fig. 3 is a cross-sectional view of the example of the pneumatic tire according to the second embodiment of the present invention (more specifically, a cross-sectional view of the tire cross section perpendicular to the tire circumferential direction).

[0126] The tire 100 shown in FIG. 3 has a pair of bead portions 10, a pair of sidewall portions 20, and a tread portion 30 continuous with both sidewall portions 20, and is equipped with: a carcass layer 50 extending in a toroidal shape between bead cores 40 embedded in the pair of bead portions 10; two belt layers 60A, 60B arranged on the tire radial outside of the crown portion of the carcass layer 50; a belt reinforcing layer (also referred to as a "cap layer") 70A arranged on the tire radial outside of the belt layers 60A, 60B so as to cover the entire belt layers 60A, 60B; a pair of belt reinforcing layers (also referred to as "layer layers") 70B arranged so as to cover only both end portions of the belt reinforcing layer 70A; and an inner liner layer 80 arranged adjacent to the carcass layer 50 on the tire inner surface side.

[0127] In the tire 100 shown in Fig. 3, the carcass layer 50 is a single layer, but in the pneumatic tire of the second embodiment of the present invention, the number of carcass layers may be two or more. In addition, in the tire 100 shown in Fig. 3, the carcass layer 50 is composed of a main body portion extending in a toroidal shape between a pair of bead cores 40 each embedded in the bead portion 10, and a folded-up portion wound up radially outward around each bead core 40 from the inner side toward the outer side in the tire width direction. However, in the pneumatic tire of the second embodiment of the present invention, the shape and structure of the carcass layer 50 are not limited to this. Here, the carcass layer 50 is preferably formed by coating a plurality of reinforcing cords that extend in a direction substantially perpendicular to the tire circumferential direction (for example, extending at an angle of 70 to 90 degrees) with a coating rubber; that is, the carcass layer 50 is preferably a radial carcass. The reinforcing cords of the carcass layer 50 are preferably the reinforcing cords containing the polyamide fibers described above, but when the reinforcing cords containing the polyamide fibers described above are applied to the belt reinforcing layers 70A, 70B, other organic fiber cords or steel cords may be used. Examples of the other organic fiber cords include polyethylene terephthalate cords and rayon cords.

[0128] 3 has two belt layers 60A, 60B, but the number of belt layers in the pneumatic tire of the second embodiment of the present invention may be one or three or more. In the tire 100 shown in FIG. 3, each belt layer 60A, 60B is usually formed by coating reinforcing cords that extend at an angle inclined with respect to the tire equatorial plane (for example, at an angle of 15 to 40 degrees) with a coating rubber, and preferably by coating steel cords with a coating rubber, and further, the two belt layers 60A, 60B are layered such that the reinforcing cords constituting the belt layers 60A, 60B intersect with each other with the tire equatorial plane in between.

[0129] In the tire 100 shown in FIG. 3 , the belt reinforcing layers 70A, 70B are formed by coating reinforcing cords with a coating rubber, the reinforcing cords being arranged substantially parallel to the tire circumferential direction (e.g., at an angle of 0 to 5° relative to the tire circumferential direction). The belt reinforcing layers 70A, 70B are formed by continuously spirally winding narrow strips of reinforcing cords coated with a coating rubber in the tire circumferential direction. In this case, the absence of joints in the tire circumferential direction improves tire uniformity, and the absence of joints also prevents strain concentration at the joints. The reinforcing cords in the belt reinforcing layers 70A, 70B are preferably reinforcing cords containing the polyamide fibers described above. However, when the reinforcing cords containing the polyamide fibers described above are used in the carcass layer 50, other organic fiber cords may also be used. Examples of other organic fiber cords include polyethylene terephthalate cords and rayon cords. 3 includes a belt reinforcing layer 70A and a belt reinforcing layer 70B, but a tire in which either one of the belt reinforcing layer 70A or the belt reinforcing layer 70B is omitted is also an example of a pneumatic tire according to the second embodiment of the present invention. In addition, in the tire 100 shown in FIG. 3, the belt reinforcing layer (cap layer) 70A and the belt reinforcing layer (layer layer) 70B each comprise one layer, but may comprise two or more layers.

[0130] 3, the tire 100 has one inner liner layer 80, but the pneumatic tire of the second embodiment of the present invention may have two or more inner liner layers. The inner liner layer 80 has the function of maintaining the internal pressure of the tire, and a rubber with low air permeability is used for the inner liner layer 80. As such a rubber with low air permeability, a rubber composition can be used in which a rubber component such as butyl rubber or halogenated butyl rubber is blended with a filler such as carbon black, an antioxidant, a vulcanizing agent such as sulfur, a vulcanization accelerator, etc.

[0131] The tire 100 shown in FIG. 3 also includes a tread rubber layer 90 located on the outermost surface of the tread portion 30. The tread rubber layer 90 can be made of a rubber composition that blends a rubber component such as natural rubber or synthetic rubber with a filler such as carbon black, an antioxidant, a vulcanizing agent such as sulfur, a vulcanization accelerator, and the like. The tread rubber layer 90 of the tire 100 shown in FIG. 3 is a single layer, but the pneumatic tire of the second embodiment of the present invention may have two or more tread rubber layers. For example, the tread rubber layer 90 of the tire 100 shown in FIG. 3 can be divided into a cap rubber located on the outermost surface side and a base rubber located radially inward of the cap rubber.

[0132] Figure 4 is an enlarged view of the area surrounded by dashed line IV in the tread portion 30 of the tire 100 shown in Figure 3. In Figure 4, the carcass layer 50 and the belt reinforcing layer 70A include reinforcement cords 50-1 and 70A-1. Here, the carcass layer 50 is composed of a reinforcement cord 50-1 and a coating rubber 50-2 that coats the reinforcement cord 50-1. Similarly, the belt reinforcing layer 70A is composed of a reinforcement cord 70A-1 and a coating rubber 70A-2 that coats the reinforcement cord 70A-1. Furthermore, at least one of the reinforcement cord 50-1 of the carcass layer 50 and the reinforcement cord 70A-1 of the belt reinforcing layer 70A contains the above-mentioned polyamide fiber having an amide density of 14.0 or less. In addition, a tire in which neither the reinforcing cord 50-1 of the carcass layer 50 nor the reinforcing cord 70A-1 of the belt reinforcing layer 70A contains polyamide fiber having an amide density of 14.0 or less, and the reinforcing cord of the belt reinforcing layer (layer) 70B not shown in Figure 4 contains polyamide fiber having an amide density of 14.0 or less, is also an example of a pneumatic tire of the second embodiment of the present invention.

[0133] 3 and 4, the tire width direction D of the tire cross section perpendicular to the tire circumferential direction Ｗ In the region R where the belt reinforcing layers 70A and 70B are arranged, ＲWhen the gauge thickness (distance) D from the outer peripheral surface of the tire outer surface side of the reinforcement cord 70A-1 of the outermost belt reinforcement layer 70A (more specifically, an imaginary line connecting the outer peripheral surfaces of the reinforcement cords 70A-1 of the belt reinforcement layer 70A on the tire outer surface side) to the tire outer surface was measured at 100 equally spaced points, 80% or more of the measurement points had a gauge thickness D of 6.0 mm or less. In Fig. 4, the gauge thickness D from the outer peripheral surface of the reinforcement cord 70A-1 on the tire outer surface side to the tire outer surface is calculated by multiplying the total thickness of the tread rubber layer 90 by the tire radial direction D Ｒ This corresponds to the total thickness of the coating rubber 70A-2 of the outermost belt reinforcing layer 70A. By ensuring that 80% or more of the measurement points have a gauge thickness D of 6.0 mm or less (i.e., by reducing the total thickness of the tread rubber layer 90 and the thickness of the coating rubber 70A-2 of the belt reinforcing layer 70A), as described above, heat generated inside the tire during running is quickly dissipated, preventing the inside of the tire from becoming too hot during running. By preventing the inside of the tire from becoming too hot during running, deterioration of the physical properties of the reinforcing cords containing polyamide fibers with an amide density of 14.0 or less is suppressed, thereby maintaining tire performance.

[0134] In the pneumatic tire according to the second embodiment of the present invention, it is preferable that the reinforcing cords of both the carcass layer 50 and the belt reinforcing layers 70A, 70B contain polyamide fibers having an amide density of not more than 14.0. When the reinforcing cords of both the carcass layer 50 and the belt reinforcing layers 70A, 70B contain polyamide fibers having an amide density of not more than 14.0, it becomes easy to apply biomass-derived polyamide fibers to the reinforcing cords of the carcass layer 50 and the belt reinforcing layers 70A, 70B, and it becomes easy to reduce the environmental load.

[0135] <Method for manufacturing pneumatic tire> Depending on the type of tire to be applied, the pneumatic tires of the first and second embodiments of the present invention may be obtained by molding and then vulcanizing an unvulcanized rubber composition or an unvulcanized treat (a cord-rubber composite in which reinforcing cords are coated with a coating rubber), or by molding and then vulcanizing a semi-vulcanized rubber that has undergone a pre-vulcanization process or the like instead of an unvulcanized rubber composition. The components of the pneumatic tires of the first and second embodiments of the present invention other than the carcass layer and the belt reinforcing layer are not particularly limited, and known components can be used. Furthermore, the gas to be filled into the pneumatic tires of the first and second embodiments of the present invention can be normal air or air with an adjusted oxygen partial pressure, or an inert gas such as nitrogen, argon, or helium.

[0136] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples in any way.

[0137] Comparative Example 1 Two 1400 dtex polyamide 6,6 (PA66) fibers (amide density 14.3) were first twisted, then paralleled and second twisted to produce a twisted cord [cord structure: 1400 / / 2 / 2]. The number of first twists was 22 per 10 cm, and the number of second twists was 22 per 10 cm.

[0138] Example 1 Two 1400 dtex polyamide 4,10 (PA410) fibers (amide density 12.5) were first twisted, then paralleled and second twisted to produce a twisted cord (cord structure: 1400 / / 2 / 2). The number of first twists per 10 cm was 22, and the number of second twists per 10 cm was 22.

[0139] <Measurement of Heat Shrinkage of Cord> According to ASTM D885 and ASTM D4974, the cord was heated at 177°C for 2 minutes to measure the heat shrinkage of the cord.

[0140] <Evaluation of Cord Properties> A tensile test was carried out on the cord obtained as described above in accordance with JIS L 1013 "Testing methods for chemical fiber filament yarns," and the load (N)-elongation (%) curve of the cord was measured. The strength (N) and elongation (%) at break at 100°C of Comparative Example 1 were set to 100, and the respective values ​​were expressed as indices.

[0141]

[0142] Comparing Comparative Example 1 with Example 1, it is clear that the cord made of PA410 fiber has a greater decrease in strength at break at high temperatures than the cord made of PA66 fiber.

[0143] In contrast, according to the first embodiment of the present invention, the average gauge thickness from the outer peripheral surface on the tire inner surface side of the reinforcing cord of the carcass layer located innermost in the tire radial direction to the tire inner surface is thinned to 1.5 mm or less, thereby quickly dissipating heat generated inside the tire during running, suppressing the inside of the tire from becoming too hot during running, and suppressing deterioration in the physical properties of the reinforcing cord containing polyamide fiber with an amide density of 14.0 or less, thereby making it possible to maintain tire performance.

[0144] Furthermore, according to the second embodiment of the present invention, when the gauge thickness of the reinforcing cord of the belt reinforcing layer located at the outermost side in the tire direction from the outer peripheral surface on the tire outer surface to the tire outer surface is measured at 100 equally spaced points, the gauge thickness of the measuring points is set to be 6.0 mm or less at 80% or more. This allows heat generated inside the tire during running to be quickly dissipated, prevents the inside of the tire from becoming too hot during running, and prevents deterioration of the physical properties of the reinforcing cord containing polyamide fiber with an amide density of 14.0 or less, thereby maintaining tire performance.

[0145] 100: Tire 10: Bead portion 20: Sidewall portion 30: Tread portion 40: Bead core 50: Carcass layer 50-1: Reinforcement cord 50-2: Coating rubber 60A, 60B: Belt layer 70A: Belt reinforcing layer (cap layer) 70A-1: Reinforcement cord 70A-2: Coating rubber 70B: Belt reinforcing layer (layer layer) 80: Inner liner layer 90: Tread rubber layer R: Region where belt reinforcing layer is arranged A: Gauge thickness (distance) from the outer peripheral surface of the inner surface of the tire of the reinforcing cord of the carcass layer located at the innermost side in the tire radial direction to the inner surface of the tire B: Total thickness of the inner liner layer C: Thickness of coating rubber of the carcass layer located at the innermost side in the tire radial direction D: Gauge thickness (distance) from the outer peripheral surface of the tire of the reinforcing cord of the belt reinforcing layer located at the outermost side in the tire radial direction to the outer surface of the tire D Ｒ : Tire radial direction D Ｗ : Tire width direction

Claims

1. A pneumatic tire comprising: at least one carcass layer having a pair of bead portions, a pair of sidewall portions, and a tread portion continuous with both sidewall portions, and extending in a toroidal shape spanning the pair of bead portions; at least one belt layer arranged radially outward of a crown portion of the carcass layer; at least one belt reinforcing layer arranged radially outward of the belt layer; and at least one inner liner layer arranged adjacent to the carcass layer on the tire inner surface side, wherein the carcass layer and the belt reinforcing layer comprise reinforcing cords, and the reinforcing cords of at least one of the carcass layer and the belt reinforcing layer comprise polyamide fibers having an amide density of 14.0 or less, and wherein, in a region of a tire cross section perpendicular to the tire circumferential direction where the belt reinforcing layer is arranged as viewed in the tire width direction, the gauge thickness of the reinforcing cord of the carcass layer located radially innermost in the tire from the outer peripheral surface on the tire inner surface to the tire inner surface is measured at 100 equally spaced points, and the average gauge thickness is 1.5 mm or less.

2. A pneumatic tire comprising: a pair of bead portions, a pair of sidewall portions, and a tread portion connected to both sidewall portions, and at least one carcass layer extending toroidally across the pair of bead portions; at least one belt layer disposed radially outward of a crown portion of the carcass layer; and at least one belt reinforcing layer disposed radially outward of the belt layer, wherein the carcass layer and the belt reinforcing layer contain reinforcing cords, and the reinforcing cords of at least one of the carcass layer and the belt reinforcing layer contain polyamide fibers with an amide density of 14.0 or less, and wherein, in a region of a tire cross section perpendicular to the tire circumferential direction where the belt reinforcing layer is disposed as viewed in the tire width direction, when the gauge thickness from the outer peripheral surface on the tire outer surface side of the reinforcing cord of the belt reinforcing layer located outermost in the tire radial direction is measured at 100 equally spaced points, 80% or more of the measurement points have a gauge thickness of 6.0 mm or less.

3. A pneumatic tire according to claim 1 or 2, wherein the reinforcing cords of both the carcass layer and the belt reinforcing layer contain polyamide fibers having an amide density of 14.0 or less.

4. A pneumatic tire according to claim 1 or 2, wherein the polyamide fiber having an amide density of 14.0 or less is polyamide 4,10 fiber.

5. The pneumatic tire according to claim 1, wherein the total thickness of the inner liner layer is 1.0 mm or less.

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